porcine PRRS, also known as Porcine Reproductive and Respiratory Syndrome (PRRS), is a disease that causes reproductive disorders (abortion, stillbirth, mummification) in sows and pigs of all ages In particular, piglets are characterized by respiratory diseases, which have now become one of the main diseases of reproductive disorders and respiratory diseases in large-scale pig farms.
Because this disease can cause immunosuppression, this disease has also become an important primary disease that induces high fever in pigs.
Clinical symptoms of PRRS
PRRS mainly affects the reproductive and respiratory systems, mainly manifested as reproductive failure of sows, high mortality of piglets before weaning, and finishing pigs. three symptoms of respiratory disease.
I. The main symptoms of sows
Depression, loss of appetite or abstinence, fever, varying degrees of dyspnea, late pregnancy (105-107 days), Abortions, premature births, stillbirths, mummified fetuses, weak litters occur in sows.
The abortion rate of sows can reach 50% to 70%, the stillbirth rate can reach more than 35%, and the mummy rate can reach 25%. The mortality rate increased significantly within 1 week after delivery (40% to 80%). A small number of sows showed postpartum agalactia, afterbirth stagnation and increased vaginal discharge.
Second, the performance of piglets
Especially for suckling pigs, the mortality rate is very high, up to more than 80%.
Clinical signs are age-related, with premature piglets dying at birth or within a few days. Most newborn piglets develop dyspnea (abdominal respiration), muscle tremors, hindquarter paralysis, ataxia, sneezing, lethargy, depression, loss of appetite or abstinence, body temperature rises above 40°C, and diarrhea.
Rough fur, progressive weight loss, and edema of the eyelids. In a small number of piglets, the ears and body surface skin were purplish.
3. Performance of fattening pigs
The body temperature can rise to about 41℃ , Appetite is significantly reduced or abolished, most of the body is red, breathing is accelerated, cough is obvious, and individual sick pigs have a small amount of mucus in the nose.
Respiratory symptoms with different procedures, a few cases may show cough and dark purple skin on the back of both ears, edges, abdomen and tail. Infected pigs are prone to secondary infection and corresponding symptoms.
4. The performance of breeding boars
The incidence rate is low, mainly manifested as general clinical symptoms, but the semen quality of boars declines, sperm deformities, Semen can be poisonous.
Why is PRRS difficult to control?
This has something to do with the characteristics of the virus. Now the research on PRRS virus has concluded that the virus has the following characteristics:
1. Variation of strains.
As an RNA virus, PRRS virus is very easy to mutate. Recombination between viruses also occurs easily, which leads to the diversity of strains;
2. Persistent infection and vertical transmission.
PRRS virus can cause persistent infection, viremia lasts for a long time, and the detoxification period lasts for a long time, so that the virus continuously circulates in the pig herd.
In addition, PRRS virus can be transmitted across the placenta, making newborn piglets with the virus and high mortality in the farrowing room.
3. As we all know, PRRS virus can lead to immunosuppression, resulting in a decline in the body’s resistance.
4. Antibody-dependent enhancement (ADE), that is, low levels of PRRS antibodies not only fail to protect pigs, but instead promote the disease. This in turn suggests to us that there is a certain risk of PRRS immunity.
5. The production of neutralizing antibodies in PRRS is delayed (generally after immunization, the time for the production of neutralizing antibodies should take at least 4-6 weeks). This is also the “smartness” of the PRRS virus. Unlike ordinary viruses, the PRRS virus does not induce a high level of neutralizing antibodies to eliminate itself.
6. Induce an inflammatory response, leading to severe clinical symptoms in the body.